Introduction to Iron-Based Superconductors

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Spin Fluctuations and Superconductivity One way <strong>to</strong> proceed (weak coupling): • Calculate matrix elements V k,k’ for a set of k,k’ on the FS. • Set-up gap equation -- diagonalize V. Berk-Schrieffer-Fay-Appel weak coupling theory, 1966-1980: + - Electron doped LaFeAsO I.I. Mazin, D.J. Singh, M.D. Johannes and M.H. Du, PRL 101, 057003 (2008) Singlet: V(q) = - I 2 (q)χ 0 (q) 1 - I 2 (q)χ 02 (q) In a singlet channel there is a minus sign for spin fluctuations (repulsive), which then favors opposite order parameters on the electron and hole sheets s +/- state. Note prior work, Aronov & Sonin (1972); Kuroki and Arita (2001) Does not have an obvious strongly q- dependent interaction for nodes in a FS.
Spin Fluctuation Driven s +/- Properties • Two gap. • SDW and superconductivity are driven by the same interaction and compete for the same electrons. • Simplest form is nodeless, but this is not essential. • Robust against low q scattering (Co, Ni doping) • No corner junction shifts (s-wave symmetry) • Coherence fac<strong>to</strong>rs depend on q. Reduced Hebel-Slichter peak in NMR relaxation rate. • Resonance peak in neutron scattering.
Page 1 and 2: Introduction to Iron-Based Supercon
Page 3 and 4: Materials LaFeAs(O,F) Basic Researc
Page 5 and 6: Discovery of Superconductivity in F
Page 7 and 8: Fe-based Superconducting Families Z
Page 9 and 10: FeSe - The “Simplest” Fe-Superc
Page 11 and 12: A Word About Structure (Ca,Sr) 2 Ru
Page 13 and 14: Phonons and Electron-Phonon Interac
Page 15 and 16: Arsenide Electronic Structure: LaFe
Page 17 and 18: Normal Metallic State • Low carri
Page 19 and 20: Coulomb Correlations • LDA and co
Page 21: LaFeAs(O,F) Lindhard Function • N
Page 25 and 26: T=7K T=50K Magnetic Resonance Sign
Page 27 and 28: Gap Structure If some compounds hav
Page 29 and 30: Gap Structure If some compounds hav
Page 31 and 32: Neutron Scattering - Magnetism & St
Page 33 and 34: Nesting, Doping and the Lindhard Fu
Page 35 and 36: NMR: Connection of SDW and SC State
Page 37 and 38: Resistivity in LaFeAsO McGuire et a
Page 39 and 40: Superconductivity in Metal Doped Ma
Page 41 and 42: The ThCr 2 Si 2 Structure Type Stab
Page 43 and 44: Is Iron Essential for Iron-Based Su
Page 45 and 46: Neutron Scattering - Structure Deta
Page 47 and 48: Quantum Critical Points and the LDA
Page 49 and 50: Properties of the Over-Doped Side:
Page 51 and 52: Possible Electron Doped Phase Diagr
Page 53: Comparison with Cuprates Cuprates F

Introduction to Iron-Based Superconductors

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